1. Field of Invention
The present invention pertains to a nonwoven primary carpet backing. More particularly, the present invention pertains to a nonwoven primary carpet backing comprising thermoplastic polymer filaments or fibers bonded by means of a binder polymer.
2. Description of Related Art
The manufacture of nonwoven primary carpet backings, with filaments or fibers of a thermoplastic polymer being bonded with the aid of, e.g., a thermoplastic polymer bonding agent, has been known for many years. For example, such manufacture is disclosed in U.S. Pat. No. 4,842,915. This patent relates to a spunbonded fabric consisting of polyester matrix filaments, which fabric is suitable to be used as a tufting base for carpets. The fabric is strengthened by means of a binding component in the form of softenable filaments, fibers, a powder and/or fine-grained granulates. The binding component consists of polypropylene with a melting range which is at least 90.degree. C. below the melting range of the polyester matrix filaments or fibers.
Over the years, nonwoven primary carpet backings have been constantly improved in order to meet the ever more stringent demands of carpet manufacturers and consumers. Of particular importance are: increasing the breaking strength and elongation at break after tufting, increasing the tear resistance after tufting and coating, generally improving the appearance of the resulting carpet, allowing effective mending of imperfections that occur during tufting, and facilitating tuftability, i.e. by providing lower tuft-needle penetration resistance and reduced needle deflection during tufting, avoiding rough back stitch, increasing stitch lock, and reducing noise during tufting.
In general, tufting reduces the breaking strength of nonwoven backings, particularly of high initial breaking strength) nonwoven backings, because of the disruption and/or damage caused by the tufting needles.
It is noted that European patent application no. EP 822283 concerns a spunbonded web comprising two types, (a) and (b), of bicomponent sheath/core filaments having a polyethylene terephthalate core which has a melting temperature higher than that of the sheath of binding polymer. The ratio by weight of the sheath polymer of the type (a) filament to the type (b) filament is in the range from 1:3 to 1:10. Over the cross-section of the web, the ratio by weight of type (a) filaments to type (b) filaments varies from 15 to 70%. This latter ratio changes through the cross-sectional planes of the web without any noticeable or distinguishable phase boundaries so as to avoid delamination. This technology, therefore, runs counter to that of the present invention, which seeks to promote delamination.
Japanese patent application JP 04-352861 concerns a nonwoven fabric composed of composite long fibers A of a polymer (a1) and a polymer (a2) having a melting point at least 30.degree. C. higher than that of polymer (a1), and composite long fibers B of a polymer (b1) and a polymer (b2) having a melting point at least 30.degree. C. higher than that of polymer (b1). Further, the melting point of polymer (b1) is at least 20.degree. C. higher than that of polymer (a1). The fabric consists of four layers, the first containing only fibers A, the second containing more fibers A than fibers B, the third containing more fibers B than fibers A, and the fourth containing only fibers B. The concentration of fibers A and fibers B varies continuously without any clear boundaries, so that no delamination occurs.
U.S. Pat. No. 3,940,302 discloses a nonwoven web, suitable for use as a primary backing for tufted carpets. The nonwoven web contains bicomponent filaments having a core of polypropylene and a sheath of copolyamide that is described in the patent as "which is capable of being rendered adhesive in pressurized saturated steam at a pressure which leaves the core component substantially unaffected", together with polypropylene homofilaments. Parallel yarns are embedded in the web in its lengthwise direction. In a preferred embodiment, the bicomponent filaments are present in a higher concentration in a thin layer at at least one of the surfaces of the product than in the center of the product so as to improve the dye uptake of the surface of the backing.
JP 09-291457 concerns a laminate comprising web layers of a composite long fiber of the side-by-side type or the sheath/core type composed of two kinds of polymers with different melting points, i.e. high-density polyethylene and high-density polypropylene. The amount of high density polyethylene is different in each web layer. The laminate has super bulkiness, feel, and tensile strength.
JP 06-128855 discloses a three layer structure nonwoven fabric comprising a surface layer, an intermediate layer, and a backside layer. The surface layer and the backside layer are composed of a conjugate type long fiber consisting of a thermoplastic polymer component A and a thermoplastic polymer component B that is incompatible with the thermoplastic polymer component A. The long fibers are bonded by the fusion bonding of component A. The intermediate layer contains fiber A, consisting of only fiber A, and fiber B, consisting of only fiber B, which fibers are formed by dividing the conjugate type long fiber. Fiber A is entangled with fiber B without substantially being fused.